首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   516465篇
  免费   41523篇
  国内免费   384篇
  2018年   6177篇
  2017年   5970篇
  2016年   9396篇
  2015年   13293篇
  2014年   14508篇
  2013年   18053篇
  2012年   19021篇
  2011年   17344篇
  2010年   12368篇
  2009年   11272篇
  2008年   13766篇
  2007年   14076篇
  2006年   13322篇
  2005年   18322篇
  2004年   16969篇
  2003年   14744篇
  2002年   12287篇
  2001年   20772篇
  2000年   20419篇
  1999年   16454篇
  1998年   5227篇
  1997年   5205篇
  1996年   4958篇
  1995年   4556篇
  1994年   4391篇
  1992年   13645篇
  1991年   13477篇
  1990年   13308篇
  1989年   13013篇
  1988年   12190篇
  1987年   11486篇
  1986年   10390篇
  1985年   10766篇
  1984年   8564篇
  1983年   7188篇
  1982年   4996篇
  1981年   4569篇
  1980年   4348篇
  1979年   8003篇
  1978年   6152篇
  1977年   5501篇
  1976年   5278篇
  1975年   6189篇
  1974年   6882篇
  1973年   6818篇
  1972年   6184篇
  1971年   5676篇
  1970年   5038篇
  1969年   4788篇
  1968年   4481篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
A formalin-fixed paraffin-embedded (FFPE) sample usually yields highly degraded DNA, which limits the use of techniques requiring high-quality DNA, such as Infinium Methylation microarrays. To overcome this restriction, we have applied an FFPE restoration procedure consisting of DNA repair and ligation processes in a set of paired fresh-frozen (FF) and FFPE samples. We validated the FFPE results in comparison with matched FF samples, enabling us to use FFPE samples on the Infinium HumanMethylation450 Methylation array.  相似文献   
82.
83.
The Biopolymer Markup Language.   总被引:6,自引:0,他引:6  
SUMMARY: An XML derived from a data model designed to be a hierarchical representation of an organism has been specified and a browser to use this language has been developed. AVAILABILITY: The language definition is available in HTML form at http://www.proteometrics.com/BIOML/. The BioML browser is available on request from the author.  相似文献   
84.
International Journal of Primatology - The selection of sleeping sites and sleeping trees in nonhuman primates is related to social and ecological factors. We investigate the role of body...  相似文献   
85.

Background  

Recent studies point to a great diversity of non-ribosomal peptide synthesis systems with major roles in amino acid and co-factor biosynthesis, secondary metabolism, and post-translational modifications of proteins by peptide tags. The least studied of these systems are those utilizing tRNAs or aminoacyl-tRNA synthetases (AAtRS) in non-ribosomal peptide ligation.  相似文献   
86.
Experiments on frogs were performed to examine the effect of the M-cholinomimetic pilocarpine on the heart. It was discovered that at concentrations of 10(-15)--10(-5) g/ml pilocarpine exerted only an adverse chronotropic effect on the perfused heart. When applied at a concentration of 10(-4) g/ml the drug produced a negative as well as a positive chronotropic effect. The latter occurred spasmodically (without progressive rise in the heart rate) in association with a slow heart rate. In some experiments such effects were preceded by a certain deceleration of the heart. In experiments with positive chronotropic effects, arrhythmias and sinoatrial dissociation were observed sometimes. Experiments with recording of the electrograms of the sinuses and lower parts showed that such effects were caused not by pacemaker acceleration but by the removal of the blockade of conduction, between the pacemaker and the atria. As far as the pacemaker is concerned, pilocarpine exerted only a negative chronotropic effect.  相似文献   
87.
88.
Effect of B. pertussis lymphocytosis-promoting factor (LPF) on the lympho-hematopoietic system of mice was studied. The injection of LPF was shown to sharply enhance endogenous colony formation and to induce a severe depletion of thymus cells, reaching its maximum of day 4. Thymocytes obtained on day 2 or 3 after the injection of LPF produced a suppressive effect on endogenous colony formation. The proliferative activity of hematopoietic stem cells sharply increased under the influence of LPF, though it had no radioprotective action. On the following day after the injection of LPF a steep rise in the number of hematopoietic stem cells was observed in the blood of mice: their content increased 20-fold in comparison with the control level. These data may be important for the evaluation of the side effects of pertussis vaccine on the lympho-hematopoietic system.  相似文献   
89.
The Expanded Programme on Immunization (EPI) whose goal is to reduce morbidity and mortality by providing children with immunizations against diphtheria, pertussis, tetanus, poliomyelitis, measles, and tuberculosis continually faces the problem of documenting immunization coverage rates. Therefore the EPI seeks simple, effective, and inexpensive methods of evaluation which could be implemented in different countries. An example of such a method is a simplified cluster sampling technique of estimation of immunization coverage through the examination of 210 children, selected randomly as 30 groups of 7 children each. In 1978-1984 more than 1000 immunization coverage surveys were performed all over the world, mainly in developing countries. In a modified way this method is also used to collect data on morbidity and mortality of certain EPI target diseases as well as diarrhoeal diseases.  相似文献   
90.
Antibodies to calcitonin, parathyroid hormone and cortisol are detected in acute stage of infection-caused bronchial asthma. The appearance of antibodies is paralleled by marked hypercalcaemia. The antibodies may bind excessive hormones in the blood, preventing further hormonal imbalance. Ten-day treatment with glucocorticoids decreased the amount of antibodies possibly due to normalization of hormonal secretion and restoration of their balance. As a result, calcium blood levels returned to normal.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号